Heart valve prostheses are known to the prior art. Essentially, such prostheses are formed of a base member having a blood passageway, means for securing the base member in position, and a valving member for controlling the flow of blood through the passageway. Typical valving members found in prior art heart valve prostheses include an occluder in the form of balls, leaflets or discs with each employing some form of retaining means to maintain the occluder in an operative relation to the passageway while allowing the occluder to move between open and closed positions to control blood flow. The retaining means have taken the form of hinge pins, cages, and projections from the base.
The deficiencies of many prior art heart valve prostheses reside in the occluder and/or the occluder retaining means. For example, a particular design may impose mechanical requirements on the retaining means necessitating the use of a material having characteristics inferior to those of another available material. Other deficiencies of prior art heart valve prostheses include inordinate size which limits their application, undesirable effects on the blood flow, localized sites of wear and fatigue, and regions of blood stagnation.
As indicated above, the material from which a heart valve prosthesis is fabricated may have a critical impact on the clinical applicability of that prosthesis. For example, pyrolytic carbon has been recognized as inert and thrombo-resistant in the body environment, and, as such, is ideal for use in prosthetic devices. However, most prior art prosthetic heart valve designs impose mechanical requirements in at least some of the elements which has prevented fabrication of the totality of the prostheses from pyrolytic carbon. A typical disc valve, for example, employs projections which engage the disc to maintain its position, the projections being deformed to accept the disc during assembly of the valve. In such a valve, the disc has been fabricated of pyrolytic carbon, but the base and projections have been formed of other materials capable of withstanding the required deformation. Alternatively, it has been suggested that the base be formed of a plurality of members which are secured to each other on assembly of the valve thereby eliminating the necessity to deform the retaining means for the occluder. This approach however, has not met with success possibly as a result of the potential for separation of the members as well as the potential for creating areas of blood stagnation. Also, the joint area of such a multi-member base prosthesis is not pyrolytic carbon. Pyrolytic carbon is coated on a substrate in a manner which is fully disclosed in U.S. Pat. No. 3,526,005, which is hereby incorporated by reference.